1. Field of the Invention
This invention relates to a rotation measuring apparatus and a displacement measuring apparatus, and particularly can be well applied to a rotary encoder and an encoder in which a light beam is caused to enter a rotary member or a moving member having an optical scale comprising, for example, a plurality of uneven light-transmitting gratings periodically provided on the outer peripheral surface or the inner peripheral surface of a cylindrical body or on a flat surface, and the light beam passed through the optical scale is utilized to detect the rotation information or the movement information of the rotary member or the moving member.
2. Related Background Art
Photoelectric rotary encoders have heretofore been utilized as means for detecting the rotational speed or the amount of fluctuation of the rotational speed of computer instruments for the driving of floppy disc, business machines such as printers, NC machine tools or capsten motors for VTR or rotary mechanisms such as rotary drums.
As a technique utilized in such encoders, there is known so-called Talbot interference proposed in Japanese Laid-Open Patent Application No. 61-10716 and Japanese Laid-Open Patent Application No. 64-176914. FIGS. 1 and 2 of the accompanying drawings are schematic views of the essential portions of a rotary encoder utilizing this Talbot interference which is shown in Japanese Laid-Open Patent Application No. 3-197818, etc.
In these figures, the reference numeral 1 designates a semiconductor laser which emits a coherent light beam of a wavelength .lambda.. The reference numeral 2 denotes a lens system for converting the divergent light beam from the semiconductor laser 1 into a convergent light beam. The semiconductor laser 1 and the lens system 2 together constitute light applying means LR. The reference numeral 3 designates an optical scale having an uneven light transmitting grating portion having a plurality of V-grooves periodically formed on the cylindrical inner peripheral surface thereof. The optical scale 3 is rotated in a direction indicated by arrow.
The optical scale 3 is formed of a light transmitting optical material. Three photodetectors 4a, 4b and 4c constituting light receiving means 4 are disposed in opposed relationship with the light applying means LR with the optical scale 3 interposed therebetween. The outputs of the photodetectors are connected to a signal processing circuit 5. The signal processing circuit 5 has a pulse counting circuit, a rotational direction discriminating circuit, a signal interpolation processing circuit, etc.
In the rotary encoder of FIGS. 1 and 2, the light beam from the light applying means LR is caused to enter an area of the optical scale 3, and the light beam light-modulated (diffracted) by the optical scale 3 is further caused to enter another area of the optical scale 3 to thereby light-modulate (deflect) the light beam. A plurality of (three) light beams having emerged from the optical scale 3 are received by the light receiving means 4, and the output signal from the light receiving means 4 is utilized to detect the rotation information of the optical scale 3.